Note: This site is using Pangolin 1.2.2 beta, which adds more controls to the top pallet.

Here an image logo is placed in the top pallet using the ttg_pallet_top_title phplugins hook.

A little custom css was also needed to remove margin from a list item.

Here's the phplugins code:

function ttg_pallet_top_title( $style, $path ) { 
  echo '

  <li><a href="http://yoursite.com"><img src="http://pangolin.barbeephoto.com/backlight/designer/?c=page&a=image&p1=8" /></a></li>

  ';
  return false;
} // END

Of course, use the url to your own image.

Here's the custom css:

 .page__pallet__top > .content > ul > li {
    margin: 0;  
}